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IS 6537:1981 is the Indian Standard (BIS) for insulating cork slabs and pipe sections. This code of practice outlines the methods for applying baked granulated cork slabs and pipe sections for thermal insulation purposes. It details the requirements for surface preparation, adhesive application, installation procedures, and protective finishes for both hot (up to 90°C) and cold surfaces. The standard also provides guidance on selecting appropriate insulation thickness to prevent condensation and control heat transfer.
Provides guidance on the use of insulating cork slabs and pipe sections.
! This standard is for natural cork insulation, which is less common today than synthetic materials like nitrile rubber or rockwool, but is still valued for its sustainable properties and specific applications (e.g., wineries).
! Proper surface preparation (clean, dry, and free of rust/grease) as per Clause 3.1 is critical for the long-term performance of the insulation system.
! The selection and application of a suitable vapour barrier (Clause 4.1.2) is the most important step for cold insulation to prevent moisture ingress and failure.
Standard Specification for Corkboard and Cork Pipe Insulation for Low-Temperature Thermal Insulation
Specifies the material properties and dimensions for cork insulation, very similar to the material referenced by IS 6537.
EN 13170:2012+A1:2015CEN (European Committee for Standardization), Europe
HighCurrent
Thermal insulation products for buildings - Factory made products of expanded cork (ICB) - Specification
The current European product specification for expanded cork insulation boards, defining performance characteristics.
BS 5422:2023BSI (British Standards Institution), UK
MediumCurrent
Method for specifying thermal insulating materials for pipes, tanks, vessels, ductwork and equipment operating within the temperature range -40°C to +700°C
A modern code of practice for insulation application, which, while material-agnostic, covers the same installation principles as IS 6537.
Key Differences
≠IS 6537 is highly prescriptive, detailing specific application methods like using hot bitumen at 180°C. Modern standards like BS 5422 are performance-based, specifying the required outcome and allowing flexibility in materials and methods.
≠The Indian standard focuses exclusively on cork. Modern codes of practice (e.g., BS 5422) are material-agnostic, providing a framework applicable to a wide range of insulating materials like mineral wool, foam glass, and plastics.
≠IS 6537 specifies hot-applied bitumen as the primary adhesive and vapour barrier. International practice now includes a vast range of specialized cold-applied adhesives, mastics, and dedicated vapour barrier membranes with defined performance characteristics.
≠Modern European standards like EN 13170 require mandatory declaration of performance characteristics based on standardized tests, such as the water vapour diffusion resistance factor (μ-value), which is not quantified in the older IS code.
Key Similarities
≈Both the IS code and international counterparts share the fundamental objective of providing guidelines for the effective installation of thermal insulation to conserve energy and control process temperatures.
≈The practice of applying insulation in multiple layers with staggered joints to eliminate thermal bridges is a core principle detailed in IS 6537 and remains a best practice in modern international codes.
≈All standards recognize the need for a protective outer finish (e.g., plaster, sheet metal cladding) to safeguard the insulation from mechanical damage, moisture ingress, and UV radiation.
≈Both IS 6537 and international standards for pipe insulation (like BS 5422) provide specific guidance for securing pre-formed pipe sections using wires or bands.
Parameter Comparison
Parameter
IS Value
International
Source
Thermal Conductivity (k-value) at mean temp ~20°C
≤ 0.050 W/m·K (derived from IS 429:1967 value of 0.043 kcal/m.hr.°C)
Typically declared as 0.038 - 0.040 W/m·K (at 10°C mean temp)
EN 13170:2012+A1:2015
Density (Heavy Grade)
190 to 240 kg/m³ (as per referenced IS 429)
176 to 224 kg/m³ (11 to 14 lb/ft³)
ASTM C640-07
Compressive Strength (at 10% deformation)
≥ 68.6 kPa (derived from IS 429 value of 0.7 kg/cm²)
≥ 100 kPa (lowest defined level is CS(10)100)
EN 13170:2012+A1:2015
Bending Strength
≥ 98 kPa (derived from IS 429 value of 1.0 kg/cm²)
≥ 100 kPa (for level BS100)
EN 13170:2012+A1:2015
Standard Slab Thicknesses
25, 40, 50, 75, 100 mm
25, 38, 51, 76, 102 mm (equivalent to 1, 1.5, 2, 3, 4 inches)
ASTM C640-07
Water Vapour Diffusion Resistance Factor (μ)
Not specified; relies on external bitumen layer.
Declared by manufacturer; typical range is 5 - 30 (dimensionless)
EN 13170:2012+A1:2015
⚠ Verify details from original standards before use
Key Values5
Quick Reference Values
Recommended maximum service temperature90 °C
Recommended minimum service temperature-180 °C
Nominal density range for material110 to 140 kg/m³
Maximum thermal conductivity at 10°C mean temp0.038 W/(m.K)
Minimum number of binding wires per section2 per 900 mm length
Tables & Referenced Sections
Key Tables
Table 1 - Recommended Thickness of Cork Insulation for Cold Pipes
Table 2 - Recommended Thickness of Cork Insulation for Cold Flat Surfaces
To provide a standard procedure for the application of cork insulation on pipes, ducts, and vessels to ensure effective and durable thermal performance. (Scope 1.1)
Is a vapour barrier required for cork on cold lines?+
Yes, a suitable vapour barrier finish is essential for all cold applications to prevent moisture ingress, which degrades insulation performance. (Clause 4.1.2)
How should multiple layers of cork insulation be installed?+
All joints in succeeding layers should be staggered with respect to the joints in the preceding layer to avoid thermal bridges. (Clause 3.3.4)
What material is recommended for the vapour barrier?+
The code suggests two coats of bituminous mastic compound applied over the insulation surface. (Clause 4.1.2)